The use of flexible printing plates is well known in the art of printing. The printing plate is typically mounted onto a cylindrically hollow and slightly more rigid print sleeve which, in turn, overlays a cylindrical print cylinder. The print cylinder, usually made of a metal material, then rotates about its longitudinal axis at relatively high speeds. Printing plates mounted to a print cylinder in this fashion are particularly useful for printing images and text on surfaces and materials that are soft, flexible and easily deformable. Such flexible surfaces and materials include packaging materials of paper, plastic films or metal foils, or materials with an irregular surface.
The use of the interposed sleeve provides a surface to which the printing plate can adhere, the print sleeve being relatively rigid in comparison to the generally flexible and pliable printing plate that is secured to it. Moreover, the interposed sleeve allows for the removal of the sleeve, and thus the printing plate, from the print cylinder in order that different print jobs can be run using the same cylinder, the cylinder being a very expansive piece of equipment. In the art, the print sleeve has an inner diameter that is slightly less than that of the outer diameter of the print cylinder. Once in place over the print cylinder, it is intended that the print sleeve frictionally adhere to the print cylinder and not be moved relative to it as the print cylinder rapidly rotates during the printing process. Due to this tight fit, methods and devices have been used to facilitate the mounting of the sleeve onto the cylinder and then the removal of the sleeve from the cylinder.
In the experience of these inventors, at least one such attempt has been made to air pressurize the inside of the print cylinder and then provide a number of small air apertures about the outer perimeter of the cylinder surface. In this fashion, pressurization of the cylinder interior works to provide air flow through the apertures and, in turn, provide the print sleeve with a layer of pressurized air to ride over. This air pressure expands the inner diameter of the sleeve ever so slightly, but enough to allow the sleeve to be placed over the cylinder in a relatively easy fashion. One disadvantage to this type of cylinder pressurization, however, is that it requires a greater volume of pressurized air to accomplish the intended purpose. That is, sufficient air flow through the apertures is only accomplished when the complete interior of the cylinder in adequately pressurized. Not only may such cylinders not qualify as certifiably safe pressure vessels, but there is additional time that is required to pressurize the entire cylinder. This takes time away from production. Additionally, the pressurized air supply typically includes air contaminants, including moisture, which, in larger volume vessels, may accumulate in the vessel and work to corrode and destroy the vessel from within.